<template>
    <ul  class="list">
      <li class="item"
          v-for="item in letters"
          :key="item"
          :ref="item"
          @touchstart.prevent="handleTouchStart"
          @touchmove="handleTouchMove"
          @touchend="handleTouchEnd"
          @click="handleLettterClick"
      >{{item}}</li>
    </ul>
</template>

<script>
    export default {
      name:'CityAlphabet',
      props:{
        cities:Object

      },
      computed:{
        letters(){
          const letters = []
          for(let i in this.cities){
                letters.push(i)
          }
          return letters
        }
      },
      data(){
          return {
            touchStatus:false,
            startY:0,
            timer:'',
          }
      },
      updated(){
        this.startY = this.$refs['A'][0].offsetTop
      },
      methods: {
        handleLettterClick(e){
            this.$emit('change',e.target.innerHTML)
        },
        handleTouchStart(){
          this.touchStatus = true
        },
        handleTouchMove(e){
          if(this.touchStatus){
            if(this.timer){
                clearTimeout(this.timer)
            }
            this.timer = setTimeout(()=>{
              const touchY = e.touches[0].clientY - 87
              const index = Math.floor((touchY-this.startY)/20)
              if(index >=0 && index < this.letters.length){
                this.$emit('change',this.letters[index])
              }
            },16)

          }
        },
        handleTouchEnd(){
          this.touchStatus = false
        }
      }
    }
</script>

<style lang="stylus" scoped>
  @import '~styles/varibles.styl'
  .list
    position: absolute
    top: 1.58rem
    right:0
    bottom:0
    width: .4rem
    display: flex
    flex-direction column
    justify-content center
    color: $bgColor
    .item
      line-height:.44rem
      text-align center

</style>
